SBX SBX Accu AND X-Register, subtract operand, result into X-Register SBX
N V - B D I Z C
Operation: X <- (X)/\(A) - M / . . . . . / /
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | SBX #$FF | $CB | 2 | 2 |
+----------------+-----------------------+---------+---------+----------+
Note: Performs CMP and DEX at the same time, so the subtraction
ignores flags 'C' and 'D' (like CMP, unlike SBC).
Also known as AXS.